Trona is a naturally occurring ore found in the area of Green River, Wyoming and Kenya, Africa. Crude trona, for example, from the state of Wyoming consists of about 90% sodium sesquicarbonate EQU NaCO.sub.3.NaHCO.sub.3.2H.sub.2 O.
The major impurities occur in the irregular seams which are commonly termed "oil shale", more accurately these can be described as marlstone rich in organic matter, approximately 4% of the ore as mined is the mineral shortite, EQU NaCO.sub.3.2CaCO.sub.3
which is relatively insoluble in water and is always associated with the oil shale. The crude ore also contains organic matter which is found in the sodium sesquicarbonate and oil shale. Iron, present mostly, as pyrite, vanadium, chromium and other heavy metals are also present as minor impurities, mixed with about 4% to 6% insoluble impurities which are largely silicates and contains small amounts of iron, sulfates, chlorides, etc. A typical reported trona analysis is 45.11% Na.sub.2 CO.sub.3, 35.75% NaHCO.sub.3, 15.32% water, 0.03% NaCl, 0.01% Na.sub.2 SO.sub.4, 0.11% Fe.sub.2 O.sub.3 and 3.75% insolubles. However, the analysis will differ depending upon the location in the mine from which the trona is removed, some portions carrying larger or smaller percentages of insolubles and other impurities.
Two basic processes have been used commercially in the processing of the ore.
One process dissolves the sesquicarbonate as such, treats the solution to remove insolubles and organic matter, and then crystallizes sodium sesquicarbonate which may be used as such or calcined to soda ash. The resultant soda ash is pseudomorphic in form after the crystal pattern of the sodium sesquicarbonate, and special additives are needed to get desirable crystal properties. Moreover, the crystal structure is different from that obtained by the conventional Solvay process, so that the product is sometimes difficult to substitute for conventional Solvay process soda ash. Processes of this type are disclosed in U.S. Pat. Nos. 2,346,140; 2,639,217; 2,798,790 and 3,028,215.
The second basic process for handling natural trona, the so-called monohydrate process, produces a product which is like Solvay process soda ash. In this process, the trona is first calcined to crude soda ash; the ash is dissolved, and the solution treated to remove insolubles. The resultant solution is crystallized to produce sodium carbonate monohydrate crystals, which are then treated to remove the water of hydration and produce soda ash. Process of this type are disclosed in U.S. Pat. Nos. 2,343,080; 2,343,081; 2,962,348; 3,131,996 and 3,260,567.
Each of these processing techniques involves dissolution, clarification, filtration and crystallization, with relatively high energy consumption, adding substantially to the cost of the final product.
Accordingly, it is an object of the present invention to provide a relatively simple and inexpensive process for the production of soda ash from trona ore.
It has now been discovered that trona can be effectively beneficiated by froth flotation using organic compounds of a specified type as flotation collectors.